Recently, Lu2SiO5:Ce(LSO), Lu2(1−x)Y2xSiO5:Ce(LYSO), LuAlO3:Ce(LuAP), LuxY1−xAlO3:Ce(LuYAP), LaCl3:Ce, LaBr3:Ce and LuI3:Ce have been known for scintillator materials for TOF-PET: time of flight positron emission computed tomography, as set out in Table 1. For instance, see Patent Publications 1, 2 and 3 as well as Non-Patent Publication 1.    Patent Publication 1: JP(A) 2007-16197    Patent Publication 2: JP(B) 2004-532997    Patent Publication 3: USP 2006/0124854A1    Non-Patent Publication 1: M. D. Birowosuto et al., J. Of App. Phys. Vol. 99, 123520 (2006)
The properties of the respective scintillator materials are set out in Table 1.
TABLE 1LightMax.QuantityEmissionDensity(Photons/DecayWavelengthSingle Crystal(g/cm3)MeV)Time (ns)(nm)Lu2SiO5: Ce7.42600040420(LSO)Lu2(1-x)Y2xSiO5: Ce7.13000040420(LYSO) @x = 0.1LuAlO3: Ce8.31100018160385(LuAP)LuxY1-xAlO3: Ce7.31300020200380(LuYAP) @x = 0.2LaCl3: Ce3.864600025 (50%)350LaBr3: Ce5.077000016 (97%)380LuI3: Ce5.6900006-40 (72%)  472
As shown in Table 1, the properties of the scintillator materials demanded for current PETs are primarily:    1. high light output (high light emission),    2. emission wavelength lying in the visible range,    3. high density (heavy crystal),    4. high serviceability, and    5. short decay time (short vanishing time).
Now, among the aforesaid scintillator materials, attention is directed to LaBr3:Ce and LuI3:Ce capable of emitting more light. However, LaBr3:Ce has the disadvantages of being not heavy, costing much, and being deliquescent with the emission wavelength lying in the ultraviolet range. On the other hand, a problem with LuI3:Ce is that it still costs much, although it emits more light than LaBr3:Ce does, with the emission wavelength lying in the visible range. Thus, the development of material that replaces LuI3:Ce as the scintillator material for the next-generation TOF-PET is in great demand.
The LuI scintillators set forth in Patent Publication 3 and Non-Patent Publication 1 are grown by the Bridgman method using LuI3 and CeI3 as the raw materials. The raw materials LuI3 and CeI3, especially LuI3 give rise to rises in the cost of the ensuing LuI scintillator, because raw materials synthesis costs much. LuI3 and CeI3, especially LuI3 may possibly degrade the ensuing LuI scintillator because of entraining impurities such as water, chlorine, bromine, etc. during the raw materials synthesis.
In other words, it would be more advantageous to produce LuI scintillators without using LuI3 as the raw material.